1. Field of the Invention
The present invention relates to a microwave oven, and more particularly, to a door assembly of a microwave oven, to prevent microwave irradiated to a cooking cavity from leaking externally.
2. Discussion of the Related Art
In general, a microwave oven melts or cooks food with frictional heat generated when vibrating molecules of food by irradiating microwave. Recently, an electric oven has been used, in which a heater is provided to cook various kinds of food. Hereinafter, the structure of general microwave and electric ovens will be described with reference to the accompanying drawings.
Referring to FIG. 1, an outer case 10 having the open front is provided in the microwave or electric oven, and a front frame 11 is provided in the circumference of the open front of the outer case 10. Then, an inner case 20 is provided in the inside of the outer case 10. At this time, an opening is provided in front of the inner case 20, and an inside space of the inner case 20 forms a cooking cavity for cooking food. Meanwhile, a door 30 is hinged on the front frame 11 so as to open and close the opening of the inner case 20.
Also, a heater 44 and a ventilating fan 46 may be provided at an upper part, a lower part, or a side part to the inner case 20. The heater 44 heats the cooking cavity 25, and the ventilating fan 46 generates a circulating air current inside the cooking cavity 25. Accordingly, food received in the cooking cavity 25 is heated with heat irradiated from the heater 44, and the hot air circulating inside the cooking cavity 25 by the ventilating fan 46.
Then, an outfit chamber 40 is provided between the outer case 10 and the inner case 20. At this time, the outfit chamber 40 is provided with a magnetron 41 for generating the microwave, a high-voltage transformer 42 for providing a high voltage to the magnetron, a wave guide 43 for guiding the microwave generated by the magnetron 41 to the cooking cavity 25, and a cooling fan 44 for cooling electric components provided in the inside of the outfit chamber 40. As shown in FIG. 1, the outfit chamber 40 may be provided at an upper part of the cooking cavity 25. Or, as shown in FIG. 2, the outfit chamber 40 may be provided at a side part of the cooking cavity 25.
In the microwave or electric oven having the aforementioned structure, when the door 30 is closed in state of having food inside the cooking cavity 25, the microwave or electric oven is put into operation. That is, the microwave generated by the magnetron 41 is irradiated to the inside of the cooking cavity 25. At this time, some of the microwave arrives on food directly (progressive wave), and the rest arrives on food after being firstly reflected by the inner surface of the inner case 20 (reflective wave). Thus, the microwave or electric oven heats food uniformly by using the microwave of multi-wavelength in which the progressive and reflective waves are compounded. In this case, the heater 44 and the ventilating fan 46 are used at need.
If the microwave irradiated to the cooking cavity 25 leaks externally, and directly irradiates the human body, it is very dangerous to the human body. Thus, it is required to provide the door 30 with a microwave-leakage prevention structure. The structure of the door will hereinafter be described with reference to FIG. 3 and FIG. 4.
Referring to FIG. 3 and FIG. 4, the door 30 is provided with a door panel 31 forming the exterior, and a door filter 35 attached to the inner surface of the door 30 so as to prevent the microwave leakage. At this time, as shown in FIG. 3, an edge 31a of the door panel 31 is in contact with the front frame 11 when the door 30 is closed, whereby the cooking cavity 25 is closed completely and tightly. Also, as shown in FIG. 4, a choke portion 35a is provided in an edge of the door filter 35, the choke portion 35a curved to the outer surface of the door 30. In this state, the choke portion 35a is provided with a plurality of linear slots 35b, and the plurality of linear slots 35b are provided at fixed intervals in a length direction of the choke portion 35a. In this structure, the choke portion 35a of the door filter 35 prevents the microwave from leaking through a gap of the door 30 to the external, thereby improving heat efficiency and safety of the cooking cavity 25.
However, the door filter 35 having the aforementioned structure according to the related art has the following disadvantages.
In the choke portion 35a, an optimum microwave-shielding frequency is changed according to an incident angle of microwave on the door 30, whereby it causes the deterioration of microwave-shielding efficiency. Hereinafter, this will be described in detail.
Referring to FIG. 5, in the door filter 35 including the choke portion 35a having the linear slot 35b, when the incident angle of microwave is at 15.6°, 21.9°, and 35.6°, a resonant point is formed at about 125 dB, 120 dB, and 90 dB, and a corresponding frequency for forming the resonant point in each incident angle is 2.5 GHz, 2.55 GHz, and 2.59 GHz. At this time, the frequency, at which the resonant point is formed, is referred to as the optimum microwave-shielding frequency. Thus, it is possible to obtain the maximum microwave-shielding efficiency at the optimum microwave-shielding frequency.
In the aforementioned door filter 35 according to the related art, the optimum microwave-shielding frequency is changed according to the incident angle of the microwave, so that the microwave may leak to the external whenever the incident angle of the microwave on the door 30 is changed. Accordingly, the microwave-shielding efficiency of the door filter 35 is deteriorated, thereby lowering manufactures' safety.
Also, in case the slot 35b extends to one portion of the door filter 35 being in contact with the cooking cavity 25 as well as to the choke portion 35a, it is possible to decrease the change of the optimum microwave-shielding frequency according to the incident angle of the microwave. In this case, moisture generated from food inside the cooking cavity 25 may come into the slot 35b, whereby it causes a user's inconvenience of cleaning the door 300.